V. To make loud high pitched noises (this includes squealing, yelling, or talking so quickly that it doesn’t sound like they are actual speaking a real language) or show their excitement for the object of their obsession though movement (this includes jumping glomping, running in circles, etc.). Fangirling involves a lot of physical action unlike fanboying and can be quite annoying.

One does not have to be a girl to start fangirling though most girls do.

v. 1. the reaction a fangirl has to any mention or sighting of the object of her "affection". These reactions include shortness of breath, fainting, highpitched noises, shaking, fierce head shaking as if in the midst of a seizure, wet panties, endless blog posts, etc.

2. a gathering of two or more fangirls in which they proceed to waste endless amounts of time ogling, discussing/arguing, stalking, etc. the object of their "affection"

The Urban Dictionary T-Shirt

The art of obsessing over fandoms, the characters in the fandoms, the actors who play the character ( if the fandom is a film/show ) etc.......
Just saying something to do with a fangirls fandom will usually lead to them frantically crashing into the room youre in making high pitched sounds that to you might sound meaningless, but to other fangirls will make total sense

Person : Dean Winchest-
*loud crashing noises*
*sound of footsteps*
Fangirl: ASDFHIHEWCBEDIHBQQDIYCBFQEYULCQGEDTOUCEDQVTOQWDVUWVUTWSYVQDWGUVWXUK WHO THE HECKLES JENSEN ACKLES SAID THE NAME OF BABY!?!?!?!?!?!?!?!?!?!
Person: fangirling again?
Fangirl: *nods while spasming on the floor*